Can Porter Airlines, the privately owned carrier flying out of Toronto's island airport, survive on flights that are only half full?

It depends on whom you ask.

Some critics who battled the decision that allowed the airline to fly out of downtown Toronto have spent the past six weeks meticulously counting the number of passengers, trying to figure out whether the airline is making enough money to stay in the air.

Bill Freeman, a spokesman for the residents' group Community Air, says the planes aren't full enough for Porter to make money, while competition with Air Canada and WestJet has grown stiffer since Porter Airline's first flight.

But Robert Deluce, president and CEO of Porter Airlines, warns critics not to count on the airline's failure.

Independent observers put the ratio of filled seats on Porter planes at about half to two-thirds, while Deluce has remained tight-lipped about numbers of passengers.

However, he has hinted the planes don't even need to be half full for the flights to be profitable.

In fact, Deluce said, the company is on track to turning a profit in its first year.

"We're very pleased with where we are now, given the very short period of time we've actually been operating," Deluce said.

Porter will begin offering flights to Montreal next week.